Embolism as main risk in case of drought
Some concepts from Yves' article
Allometric relationships and vulnerability
Sun vs Shade
Things that can still be done
Start

MOC: ARCHI
Source: millanDecipheringGrowthForm2019
Auteur: Malo
Date: 202501271640


Branching patterns in Thymus vulgaris

Acrotonic, mesotonic, basitonic (Branching patterns-Acrotonic, mesotonic, basitonic)study of thyme along water gradient.

In hot and dry habitats, higher proportion of basitonic individuals than in colder and humid habitats.
Mesotonic and acrotonic individuals relatively more present in colder and more humid habitat.

In stressed environments, thyme tends to go back to the bottom of the main stem to branch again.

Pasted image 20250127153538.png

These forms may therefore have functional advantages according to the habitat where they grow: competition for light, herbivores (haven't foud herbivores on Cistaceae yet).
Abiotic factors: soil, temperature, humidity, etc.

While there are contrasting conditions between the 2 habitat types, it might be that low-light environments, favoring tall herbs, might enter in competition for light, pushes thyme to have an acrotonic and mesotonic architecture, to position their crown above the herbaceous species

Architectural differences and variability in the relationship with light between open - closed environments in savanna: basitonic architectures capable of lateral spreading, effectively occupying space around them.

Keep in mind: unsure if the variation observed here is plasticity or genetic variation

Branching patterns in Thymus vulgaris

MOC: ARCHI
Source: millanDecipheringGrowthForm2019
Auteur: Malo
Date: 202501271708


Reiteration processes in Thymus vulgaris

Delayed reiteration process: plant’s response to injury and traumatism (loss / death of meristems, cavitation / embolism, disease, mechanical damage)

Reiteration processes in Thymus vulgaris

MOC: ARCHI
Source: millanDecipheringGrowthForm2019
Auteur: Malo
Date: 202501271641


Branching patterns: Acrotonic, mesotonic, basitonic

Branching patterns-Acrotonic, mesotonic, basitonic

MOC: || ARCHI
Source: barthelemyPlantArchitectureDynamic2007
Auteur: Malo
Date: 202501281153


Orthotropy and plagiotropy

"Orthotropy (Fig. 14A; Frank, 1868; Koriba, 1958) refers to axes whose general orientation is vertical and whose symmetry is radial, with leaves in a spiral, opposite or verticillate disposition, and associated lateral branches arranged in all spatial directions. Plagiotropic axes (Fig. 14B; Frank, 1868; Koriba, 1958) have a general horizontal to slanted orientation and a bilateral symmetry owing to leaves (distichous phyllotaxis) and branches being generally arranged in one plane."
barthelemyPlantArchitectureDynamic2007-image-12-x54-y194.png

Orthotropy and plagiotropy

Discussion avec Yves : C'est la marque de ce que la plante a subi, pousser l'analyse vers ça

Architectural differences in sun vs. shade

ARCHI

I. In-text annotations

"In the latter case, one, two or more branches may develop after the death, abscission, abortion or transformation of the apex, and the resulting sympodial branching pattern be qualified respectively as mono-, di- or polychasial." Page 381

"Acrotony is the preferred development of lateral axes in the distal part of a parent axis or shoot" Page 383

"Orthotropy (Fig. 14A; Frank, 1868; Koriba, 1958) refers to axes whose general orientation is vertical and whose symmetry is radial, with leaves in a spiral, opposite or verticillate disposition, and associated lateral branches arranged in all spatial directions. Plagiotropic axes (Fig. 14B; Frank, 1868; Koriba, 1958) have a general horizontal to slanted orientation and a bilateral symmetry owing to leaves (distichous phyllotaxis) and branches being generally arranged in one plane." Page 384

III. Persistent notes - End

barthelemyPlantArchitectureDynamic2007

MOC: ANAT || ARCHI
Source: vilagrosaXylemCavitationEmbolism2012
Auteur: Malo
Date: 202501281131


vilagrosaXylemCavitationEmbolism2012-image-5-x43-y421.png
Nice table with recap of stress tolerance / avoidance and traits that can be used to measure them Traits to measure:

  • Extensive root system
  • High water transport capacity
    • Maybe interesting to see if Helianthemum has higher Kth? If the species is only present in drier conditions, maybe more adapted for these conditions
  • High resistance to xylem cavitation
Drought resistance strategies and main mechanisms evolved

MOC: ARCHI
Source: archibaldGrowingTallVs2003
Auteur: Malo
Date: 202501271613


Open: light is not a selective pressure on tree growth form
Greater variation in tree forms is expressed
Fire frequency: selective for vertical growth (not important for our case)

Closed: heavy browsing selects for lateral growth

Architectural differences and variability in the relationship with light between open - closed environments in savanna

MOC: || ANAT
Source: anfodilloTreeMortalityTesting2021
Auteur: Malo
Date: 202501281638


Plant height, vessel size, moisture conditions and vulnerability

For a given plant height, individuals with larger conduits would be more vulnerable than individuals with narrower conduits (gleasonWeakTradeoffXylem2016, considering that Conductivity - safety trade-off is somewhat accurate).

With moist conditions, there is less risk of embolism, permitting wider conduits.

Based on the principle that Plant height is linked to wider conduits:
Once drought hits, big conduits with excessive size given the circumstances, become unusable --> re-sprouting at lower heights is therefore preferred. This gives for narrower, more embolism-resistant conduits better-suited for drier conditions.

Plant height, vessel size, moisture conditions and vulnerability

MOC: || ANAT
Source: Malo
Auteur: Malo
Date: 202501291032


Indirectly, we can imagine that taller individuals, which are more vulnerable to embolism and drought stress (Plant height, vessel size, moisture conditions and vulnerability, Plant height is linked to wider conduits) are more dependent on their mycorrhiza community, which dampen the effect that drought might have.

Do bigger individuals have a more developed mycorrhiza community?

Impact of mycorrhizae on stress tolerance with taller individuals

MOC: || ANAT
Source: anfodilloTreeMortalityTesting2021
Auteur: Malo
Date: 202501281612


Looking around species, wider conduits allow for greater conductive path, which then allows for taller plants (olsonPlantHeightHydraulic2018)

Makes it interesting to weigh vessel size with plant height: what does it show? Traits to measure

"Accordingly, across species, by far stem length is the variable that best predicts conduit diameter (r2≈0.6–0.9) (Anfodillo et al., 2006; Rosell and Olson, 2014; Olson et al., 2018, 2020b), as well as tip-to-base within individuals (r2≈0.8–0.9) (Anfodillo et al., 2006; Koçillari et al., 2021)".
Even within a species, taller individuals are therefore more vulnerable to embolism than smaller ones in the same conditions.
In this case, we can imagine the Impact of mycorrhizae on stress tolerance with taller individuals

Plant height is linked to wider conduits

MOC: ANAT
Source: riegerRootSystemHydraulic1999
Auteur: Malo
Date: 202501271530


Negative correlation between root diameter and conductivity

Negatively correlated to root diameter in this study: goes against previous study (Newman, 1973), who reported that Kth did not correlate with root anatomical features.

Negative correlation between root diameter and conductivity

Au fil du temps, une plante a dans tous les cas + de communautés
c'est un peu invérifiable
mais: si communauté myco + diversifiée : apport hydrique + importante et + stable dans le temps, plus résiliente face aux perturbations, sécheresses intenses sur les terrasses

Architecture and anatomy summary

ANAT

MOC: || ARCHI
Source: valladaresFunctionalEcologyShoot1998
Auteur: Malo
Date: 202501281202


Orthotropy and plagiotropy
Shoots present in the sun were orthotropic, with steep (71°) phyllotaxy, short internodes.
Shoots present in the shade were plagiotropic, with low angle (5°) phyllotaxy

valladaresFunctionalEcologyShoot1998-image-4-x291-y254.png

Orthotropy resulted in low efficiency in light absorption, while plagiotropy maximized efficiency.

Linked with leaf plasticity:

  • Sun leaves had higher photosynthetic capacities per unit area, higher LMA and lower respiration per area than shade leaves

--> Maximizing C gain for the smaller amount of photon that the leaf receives

Differences in ortho-plagiotropy in sun vs shade individuals and functional implications

MOC: ARCHI
Source: gignouxAllocationStrategiesSavanna2016
Auteur: Malo
Date: 202501280944


Biomass, allocation, and shape changes following light and fire treatment

Architectural differences and variability in the relationship with light between open - closed environments in savanna
In this study, savanna species responded to the shading treatment, while forest species were not impacted.

Forest species might be storing reserves in their stems rather than in their roots
While fire is the dominant factor shaping savanna seedling performance in comparison to forest species, competition for light is important to consider --> present in both ecosystems.

Concerning shape:
Cylindrical stem is better to go into great heights (more important for trees)
Conical shape (thicker) is good for reducing stem biomass loss through fires
Thicker might be better to reduce water stress?

Biomass, allocation, and shape changes following light and fire treatment

Angiosperm phylogeny website
mobot.org/MOBOT/research/APweb/

MOC: ANAT
Source: martinez-vilaltaXylemHydraulicProperties2002
Auteur: Malo
Date: 202501281100


There are several arguments explaining why roots usually have lower safety margins, in the framework of Conductivity - safety trade-off:

  1. Xylem embolism is easier to reverse, because higher (near-positive) pressures are much more frequent in roots
  2. Root xylem easier to replace through re-growth
  3. Roots are cheaper than stems or branches in C investment
  4. If very dry: can be advantageous to lose parts of the root system which are in contact with very dry portions of the soil
Narrower safety margins in roots

MOC: || ANAT
Source: torres-ruizDifferencesFunctionalXylem2017
Auteur: Malo
Date: 202501281703


READ MORE STUFF!!!!!

High vessel density might raise embolism risks contrary to conductivity - safety trade-off hypothesis wheelerIntervesselPittingCavitation2005

"Lower embolism resistances have been observed for species with both higher areas of pit membranes connecting vessels (‘rare pore’ hypothesis, Wheeler et al. 2005) and lower wood densities (Hacke and Sperry 2001, Domec et al. 2010)".

In this study, vessel size was not linked with embolism, while the distance between each vessel might be important, due to possible spread of embolism between vessels. Hence, vessel density might play a role in hydraulic safety against embolism. Wrong, this is not what the paper is saying, I misunderstood

To put in contrast with Conductivity - safety trade-off

Rare pore hypothesis

Analyse micro des mycorhizes:
Spatialisation du système racinaire : prendre x et y pour les racines

Plus de réseaux myco au niveau proximal des plantes

!!! Retrouver article de niches écologiques racinaires en conditions méditerranéennes: article archi

Plus la canopée est grande, plus elle se fait de l'ombre, plus c'est fermé, plus ça crée un micro-climat : à lier avec données environnementales

Variables intéressantes :

  • Taille canopée
  • Hauteur tige principale : + elle est haute, - il y a un effet canopée forte
  • Taille canopée pondérée par hauteur tige principale
  • et pondéré par distance du système racinaire
  • = Indice capacité à retenir l'eau (limiter l'évapo-transpi en se faisant son propre ombrage) : volume canopée, on peut avoir le z en postulant que c'est la même chose que le y, pondérée par hauteur tige principale
  • Autre indice : ratio de diamètre canopée VS diamètre du système racinaire: allocation spatiale

indices à faire en intra- et inter-spécifique: ex thymi, différence de posture entre T et F

Faire un schéma de chaque variable au sein de la plante: dessine une plante et montre où sont les variables: récapituler d'où viennent les variables

MOC: || ANAT
Source: avilaRelativeAreaVessels2023
Auteur: Malo
Date: 202501291607


There are quite some hints suggesting that vessel density raises the risk of embolism spread

  • Tissues other than xylem, which contribute very little to water transport (fibers, parenchyma), may impair gas spread through the xylem. This can lower the negative pressure needed for Definitions of cavitation and embolism to happen.
  • Inversely, gas spreads more easily if vessels are close to one another, with no additional tissues in-between them.
  • Species with more lignified vessels are less vulnerable to embolism

Can be linked to Conductivity - safety trade-off: less vessels (= less conductivity) means more safety thanks to extra tissues preventing gas from spreading through vessels.

Embolism spreading and vessel density

MOC: ANAT
Source: martinez-vilaltaXylemHydraulicProperties2002
Auteur: Malo
Date: 202501281056


Based on the principle that there is a higher risk of xylem embolism if conductivity is high, due to bigger vessels and less parenchyma. Definitions of cavitation and embolism

Negative relationship between hydraulic conductivity and resistance to embolism: trade-off between conductivity and safety.

The concept is controversial: it might be that the link between embolism and conductivity is due mainly to phylogenetic and biogeographical reasons, as is often the case with wood anatomical traits baasSystematicPhylogeneticEcological1982a.

Conductivity - safety trade-off

Comment pondérer ? Relation taille-vaisseaux ne doit pas être tout à fait linéaire

MOC: ARCHI
Source: archibaldGrowingTallVs2003
Auteur: Malo
Date: 202501271613


Branching ratio

"This is a ratio of the length of the longest branch (shoot length) and the total length of all the shoots on the branch unit (total length) (see Fig. 1). It is a measure of ramification and indicates whether growth is in the form of shoot elongation or lateral branching for each tree. It was measured on a randomly chosen branch of standard basal diameter 1.2 cm. Precision: 5 cm".

Screenshot from 2025-01-27 10-59-08.png

Branching ratio

Anat

Archi

gignouxAllocationStrategiesSavanna2016-image-4-x150-y450.png

Traits to measure

aussi faire ratio hauteur / largeur de la plante

MOC: ANAT
Source: vilagrosaXylemCavitationEmbolism2012
Auteur: Malo
Date: 202501281126


Embolism as the main risk for plant death in stressed environments

"if the tension in the xylem conduits becomes too high, thus xylem cavitation can occur i.e., water column breakage" Page 63

Cavitation = Physical occurrence of air bubbles forming in conductive tissues Page 63

"This results in the hydraulic disconnection of leaves and above-ground parts from roots because xylem conduits are filled with air and water vapor, and this phenomenon is called embolism" Page 63

Embolism = Biological phenomenon of disconnection of roots to higher organs Page 63

Definitions of cavitation and embolism
Linking back to mycorrhizae
Not so applicable in Cistaceae, especially acrotony
Plagiotropy not present in Cistaceae either
We can't obtain root biomass anymore